{"id":3117,"date":"2026-04-30T07:41:41","date_gmt":"2026-04-30T07:41:41","guid":{"rendered":"https:\/\/lightingrecipe.com\/?p=3117"},"modified":"2026-04-30T07:42:28","modified_gmt":"2026-04-30T07:42:28","slug":"caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing","status":"publish","type":"post","link":"https:\/\/lightingrecipe.com\/zh\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/","title":{"rendered":"CAF, CS, EML, EDI\/DER\u2026 are these commonly referenced metrics actually talking about the same thing?"},"content":{"rendered":"<figure class=\"wp-block-image size-large\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1024\" height=\"317\" src=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3-1024x317.jpg\" alt=\"\" class=\"wp-image-3118\" srcset=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3-1024x317.jpg 1024w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3-300x93.jpg 300w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3-768x238.jpg 768w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3-1536x476.jpg 1536w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3-18x6.jpg 18w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3-1140x353.jpg 1140w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3-600x186.jpg 600w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3.jpg 1858w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p style=\"font-size:15px\">In recent years, more and more terms that <em>sound highly technical<\/em> have emerged in the lighting industry: CAF, CS, EML, m-EDI, EDI, DER\u2026<\/p>\n\n\n\n<p style=\"font-size:15px\">Many manufacturers, designers, consultants, and system providers have heard of them\u2014and to some extent, used them. But if we push one step further and ask:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">What exactly does each of these metrics describe?<\/li>\n\n\n\n<li style=\"font-size:15px\">Are they actually talking about the same thing?<\/li>\n\n\n\n<li style=\"font-size:15px\">Can they be used interchangeably?<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">The answers are often far less clear than people assume. This reflects a very typical situation in today\u2019s lighting industry: There are more and more terms, but a true common language has not yet been established.<\/p>\n\n\n\n<p style=\"font-size:15px\">If the industry genuinely wants to move from simply \u201clighting up spaces\u201d to <strong>accurately understanding how light affects people<\/strong>, then the first step is not to invent yet another new term.<\/p>\n\n\n\n<p style=\"font-size:15px\">It is to <strong>put these commonly used metrics back into their proper context<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">Are these metrics really describing the same thing?<\/h4>\n\n\n\n<p style=\"font-size:15px\">Let\u2019s start with the conclusion: CAF, CS, EML, and EDI\/DER are not different names within the same framework.<\/p>\n\n\n\n<p style=\"font-size:15px\">They originate from:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">different stages<\/li>\n\n\n\n<li style=\"font-size:15px\">different objectives<\/li>\n\n\n\n<li style=\"font-size:15px\">different modeling approaches<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">Some function more like <strong>spectral efficacy ratios<\/strong>.<br>Some behave more like <strong>physiological response models<\/strong>.<br>Some are closer to <strong>application-level compromise metrics<\/strong>.<br>And others are more like <strong>standardized, computable, and transferable baseline coordinates<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">So the issue is not whether these terms should exist<\/h4>\n\n\n\n<p style=\"font-size:15px\">The real issue is this: If the industry treats all of them as interchangeable \u201chealthy lighting metrics,\u201d confusion becomes inevitable.<\/p>\n\n\n\n<p style=\"font-size:15px\">But if each metric is placed back into its proper role, many of the current ambiguities start to resolve themselves.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" width=\"1024\" height=\"577\" src=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/2-3-1024x577.jpg\" alt=\"\" class=\"wp-image-3119\" srcset=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/2-3-1024x577.jpg 1024w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/2-3-300x169.jpg 300w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/2-3-768x432.jpg 768w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/2-3-18x10.jpg 18w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/2-3-1140x642.jpg 1140w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/2-3-600x338.jpg 600w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/2-3.jpg 1364w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">Why is traditional lighting language no longer sufficient?<\/h4>\n\n\n\n<p style=\"font-size:15px\">In the past, the most familiar language of lighting was built around:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">illuminance<\/li>\n\n\n\n<li style=\"font-size:15px\">luminance<\/li>\n\n\n\n<li style=\"font-size:15px\">correlated color temperature (CCT)<\/li>\n\n\n\n<li style=\"font-size:15px\">color rendering (CRI)<\/li>\n\n\n\n<li style=\"font-size:15px\">light distribution<\/li>\n\n\n\n<li style=\"font-size:15px\">glare<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">These metrics are still essential. They primarily serve <strong>visual tasks and spatial quality<\/strong>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">Can we see clearly?<\/li>\n\n\n\n<li style=\"font-size:15px\">Is it comfortable?<\/li>\n\n\n\n<li style=\"font-size:15px\">Are colors accurate?<\/li>\n\n\n\n<li style=\"font-size:15px\">Is the space bright enough?<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">But the scope of lighting has expanded<\/h4>\n\n\n\n<p style=\"font-size:15px\">A growing body of research now shows that light also affects:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">circadian rhythms<\/li>\n\n\n\n<li style=\"font-size:15px\">alertness<\/li>\n\n\n\n<li style=\"font-size:15px\">emotional experience<\/li>\n\n\n\n<li style=\"font-size:15px\">even certain behaviors and physiological responses<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">Standards and position statements from the International Commission on Illumination have clearly indicated that: the traditional <strong>photopic system<\/strong> is not sufficient to fully describe human responses related to ipRGCs (intrinsically photosensitive retinal ganglion cells).<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">This changes the fundamental questions<\/h4>\n\n\n\n<p style=\"font-size:15px\">The industry can no longer stop at asking:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">\u201cHow many lux is this space?\u201d<\/li>\n\n\n\n<li style=\"font-size:15px\">\u201cIs it 3000K or 4000K?\u201d<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">Instead, it needs to ask:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">Which photoreceptive channels is this light stimulating?<\/li>\n\n\n\n<li style=\"font-size:15px\">What does this imply for vision, circadian regulation, and emotional response?<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">This is the real context behind new metrics<\/h4>\n\n\n\n<p style=\"font-size:15px\">This shift is precisely why metrics like:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">CAF<\/li>\n\n\n\n<li style=\"font-size:15px\">CS<\/li>\n\n\n\n<li style=\"font-size:15px\">EML<\/li>\n\n\n\n<li style=\"font-size:15px\">EDI \/ DER<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">have emerged.<\/p>\n\n\n\n<p style=\"font-size:15px\">They are not just \u201cnew terminology,\u201d but attempts to extend lighting language from: <strong>visual description \u2192 human biological interaction<\/strong><\/p>\n\n\n\n<p style=\"font-size:15px\">In other words: from \u201chow the space looks\u201d to \u201chow light actually affects people.\u201d<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" width=\"1024\" height=\"873\" src=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/12-1024x873.png\" alt=\"\" class=\"wp-image-3121\" srcset=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/12-1024x873.png 1024w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/12-300x256.png 300w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/12-768x654.png 768w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/12-14x12.png 14w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/12-1140x971.png 1140w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/12-600x511.png 600w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/12.png 1359w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p style=\"font-size:15px\">The human eye doesn\u2019t just \u201csee\u201d \u2014 it also \u201cfeels\u201d light.<\/p>\n\n\n\n<p style=\"font-size:15px\">In the lighting industry, the most commonly discussed elements are rods and cones. That\u2019s not wrong.<\/p>\n\n\n\n<p style=\"font-size:15px\">Rods are mainly associated with low-light (scotopic) vision. Cones are responsible for color, detail, central vision, and typical daytime visual functions.<\/p>\n\n\n\n<p style=\"font-size:15px\">But today we know that, beyond rods and cones, there is another critically important photoreceptive pathway in the human eye: ipRGCs (intrinsically photosensitive retinal ganglion cells).<\/p>\n\n\n\n<p style=\"font-size:15px\">These are associated with melanopsin, are more sensitive to short wavelengths, and are closely related to non-visual responses such as circadian rhythms, pupil response, and alertness.<\/p>\n\n\n\n<p style=\"font-size:15px\">However, to be more precise, what truly needs to be considered is not three systems, but five classes of photoreceptor channels: S-cone, M-cone, L-cone, Rod, and Melanopsin \/ ipRGC.<\/p>\n\n\n\n<p style=\"font-size:15px\">What CIE S 026:2018 establishes is a standardized metrology framework based exactly on these five photoreceptors.<\/p>\n\n\n\n<p style=\"font-size:15px\">In other words, for the first time, the industry has a shared language that is not only about \u201cwhat can be seen,\u201d but about \u201chow light stimulates the five types of receptors.\u201d<\/p>\n\n\n\n<p style=\"font-size:15px\">This is a critical shift. Because it means the lighting industry is moving from \u201cspatial output\u201d to \u201chuman input.\u201d<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">What do CAF, CS, and EML actually represent?<\/h4>\n\n\n\n<h4 class=\"wp-block-heading\">1. CAF: closer to a \u201cspectral efficiency ratio\u201d mindset<\/h4>\n\n\n\n<p style=\"font-size:15px\">CAF (Circadian Action Factor) has long been used to compare the potential of different spectra to stimulate circadian-related responses.<\/p>\n\n\n\n<p style=\"font-size:15px\">Its core logic is straightforward: under the same visual lighting conditions, is this spectrum more biased toward \u201ccircadian effect\u201d or \u201cvisual effect\u201d?<\/p>\n\n\n\n<p style=\"font-size:15px\">So CAF is essentially a weighted efficiency ratio. It helps compare different SPDs under the same photopic lux to determine which produces stronger circadian-related stimulation.<\/p>\n\n\n\n<p style=\"font-size:15px\">This approach is not without value. Its advantages are simplicity, intuitiveness, and suitability for early-stage comparisons.<\/p>\n\n\n\n<p style=\"font-size:15px\">But it also has clear limitations:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">First, it reflects spectral properties rather than actual human exposure dose.<\/li>\n\n\n\n<li style=\"font-size:15px\">Second, it does not inherently include time, spatial context, viewing direction, or actual eye exposure.<\/li>\n\n\n\n<li style=\"font-size:15px\">Third, it is not the primary shared language in current international standards.<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">So CAF helps you understand \u201chow biased a spectrum is,\u201d but it is not suitable as a complete coordinate for human response.<\/p>\n\n\n\n<p style=\"font-size:15px\">CAF is more like a <strong>spectral screening tool<\/strong>, not a full human-centric lighting language.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">2. CS: closer to a \u201cspecific physiological response model\u201d<\/h4>\n\n\n\n<p style=\"font-size:15px\">CS (Circadian Stimulus) has also had significant influence in recent years, especially in North America. Its logic differs fundamentally from CAF.<\/p>\n\n\n\n<p style=\"font-size:15px\">Rather than being a simple ratio, CS attempts\u2014through a circadian phototransduction model\u2014to map spectral stimuli onto a response scale related to melatonin suppression.<\/p>\n\n\n\n<p style=\"font-size:15px\">UL\u2019s DG 24480 also proposes design targets based on this type of framework. The strength of CS is that: It goes beyond saying \u201cmore or less biased,\u201d and tries to quantify \u201chow strong the circadian system stimulation is.\u201d<\/p>\n\n\n\n<p style=\"font-size:15px\">But this is also where the challenge lies. Once a metric moves from \u201cdescribing input\u201d to \u201cpredicting response,\u201d it inevitably introduces modeling assumptions:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">What spectral sensitivity functions are used<\/li>\n\n\n\n<li style=\"font-size:15px\">How rod, cone, and melanopsin interactions are handled<\/li>\n\n\n\n<li style=\"font-size:15px\">How dose-response is defined<\/li>\n\n\n\n<li style=\"font-size:15px\">How exposure duration is treated<\/li>\n\n\n\n<li style=\"font-size:15px\">How pupil state, timing, and exposure history are incorporated<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">As a result, CS has been accompanied by considerable methodological debate.<\/p>\n\n\n\n<p style=\"font-size:15px\">So a fair summary would be: CS is important, but it is better suited as an <strong>application-layer or response-layer model<\/strong>, rather than a foundational common coordinate system for the entire industry.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">3. EML: closer to a \u201ctransitional language for application\u201d<\/h4>\n\n\n\n<p style=\"font-size:15px\">EML (Equivalent Melanopic Lux) has been widely promoted in application contexts such as WELL.<\/p>\n\n\n\n<p style=\"font-size:15px\">Its key contribution is that it helped many people realize, for the first time: <strong>Not all lux are the same.<\/strong><\/p>\n\n\n\n<p style=\"font-size:15px\">From a communication and adoption standpoint, EML has played a significant role. It translates complex spectral\u2013receptor relationships into a format that is easier to understand and specify in project requirements.<\/p>\n\n\n\n<p style=\"font-size:15px\">However, from a stricter standardization perspective, EML is not the ideal end state. The industry has increasingly shifted toward melanopic EDI, and further toward the more comprehensive \u03b1-opic EDI \/ DER framework, because these align better with the standardized structure defined in CIE S 026 and enable consistent use across organizations and systems.<\/p>\n\n\n\n<p style=\"font-size:15px\">So in one sentence: EML is a <strong>bridge<\/strong> toward human-centric lighting\u2014but not the most suitable final coordinate system.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">Why are EDI \/ DER closer to a true coordinate system?<\/h4>\n\n\n\n<p style=\"font-size:15px\">Because they resemble a system that can be recorded, compared, and transmitted\u2014like a \u201cspectrum.\u201d<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">1. EDI: describing \u201cequivalent stimulus dose\u201d<\/h4>\n\n\n\n<p style=\"font-size:15px\">EDI (Equivalent Daylight Illuminance) can be understood as: How much illuminance from standard daylight (D65) would be required to produce the same level of stimulation for a given photoreceptor?<\/p>\n\n\n\n<p style=\"font-size:15px\">This allows results from different spectra to be compared within a unified framework.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">2. DER: describing \u201cstimulation efficiency\u201d<\/h4>\n\n\n\n<p style=\"font-size:15px\">DER (Daylight Efficacy Ratio) can be understood as: How efficient a given light is, per unit of photopic illuminance, at stimulating a specific photoreceptor.<\/p>\n\n\n\n<p style=\"font-size:15px\">CIE TN 015:2023 clearly defines the relationship: <strong>melanopic EDI = illuminance \u00d7 melanopic DER<\/strong><\/p>\n\n\n\n<p style=\"font-size:15px\">Together, these two quantities are powerful:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">EDI reflects the <strong>actual dose reaching the human body<\/strong><\/li>\n\n\n\n<li style=\"font-size:15px\">DER reflects the <strong>intrinsic efficiency of the light spectrum<\/strong><\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">One is exposure-focused, the other is source-focused. This combination is exactly what manufacturers, designers, control systems, and simulation tools need.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">Why move from single m-EDI toward a full EDI \/ DER framework?<\/h4>\n\n\n\n<p style=\"font-size:15px\">This is not a rejection of melanopic metrics. In fact, many recent consensus recommendations are indeed centered on melanopic EDI.<\/p>\n\n\n\n<p style=\"font-size:15px\">For example, Brown et al. (2022) suggest indoor light exposure guidelines such as:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">At least 250 lx during the day<\/li>\n\n\n\n<li style=\"font-size:15px\">Preferably below 10 lx in the evening<\/li>\n\n\n\n<li style=\"font-size:15px\">As close to 1 lx as possible at night<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">These are important. But looking further ahead: Humans do not respond to light through melanopsin alone.<\/p>\n\n\n\n<p style=\"font-size:15px\">Visual performance, color discrimination, adaptation, spatial perception, aspects of emotional experience, and more complex neural responses all involve the combined action of rods, S\/M\/L cones, and ipRGC pathways.<\/p>\n\n\n\n<p style=\"font-size:15px\">So if the industry aims to build a future-oriented human-centric lighting coordinate system, focusing only on m-EDI is not enough.<\/p>\n\n\n\n<p style=\"font-size:15px\">What we need is a more complete EDI \/ DER framework: Not just melanopic\u2014but incorporating stimulation across all five photoreceptor classes into a unified language.<\/p>\n\n\n\n<p style=\"font-size:15px\">This does not mean every project must present all five values. It means: The foundational language of the industry should leave room for a complete human model.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">From \u201cselling light\u201d to \u201cdescribing humans\u201d: the industry needs a new staff notation<\/h4>\n\n\n\n<p style=\"font-size:15px\">I like to use an analogy: EDI \/ DER in human-centric lighting is like musical notation in music.<\/p>\n\n\n\n<p style=\"font-size:15px\">Musical notation is not the music itself, but it is the foundational language that allows music to be recorded, transmitted, reproduced, and collaboratively created.<\/p>\n\n\n\n<p style=\"font-size:15px\">EDI \/ DER is similar.<\/p>\n\n\n\n<p style=\"font-size:15px\">It is not sleep itself.<br>Not emotion.<br>Not comfort.<br>Not spatial aesthetics.<\/p>\n\n\n\n<p style=\"font-size:15px\">But it provides a way to more precisely describe: <strong>What this light is doing to the five photoreceptive channels of the human body.<\/strong><\/p>\n\n\n\n<p style=\"font-size:15px\">With such a coordinate system, many long-standing ambiguities in the industry can finally be addressed collaboratively:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">LED manufacturers can provide more meaningful spectral data<\/li>\n\n\n\n<li style=\"font-size:15px\">Luminaire manufacturers can define products in terms of human impact<\/li>\n\n\n\n<li style=\"font-size:15px\">Control systems can move beyond brightness and CCT to modulating receptor stimulus<\/li>\n\n\n\n<li style=\"font-size:15px\">Simulation tools can evolve from illuminance-based to human-input-based modeling<\/li>\n\n\n\n<li style=\"font-size:15px\">Designers can move from \u201cfeels healthier\u201d to \u201cdesigning with coordinates\u201d<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">Without such a system, the industry easily remains stuck in vague language:<\/p>\n\n\n\n<p style=\"font-size:15px\">More natural<br>Closer to daylight<br>More circadian-friendly<br>More comfortable<br>Healthier<\/p>\n\n\n\n<p style=\"font-size:15px\">These terms are not useless\u2014but without an underlying framework, they struggle to become a shared language across organizations and product chains.<\/p>\n\n\n\n<p style=\"font-size:15px\">The real value of EDI \/ DER lies in this: For the first time, <strong>\u201chow light affects humans\u201d can be written down\u2014like a score.<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"456\" src=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/5-1024x456.png\" alt=\"\" class=\"wp-image-3123\" srcset=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/5-1024x456.png 1024w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/5-300x134.png 300w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/5-768x342.png 768w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/5-1536x684.png 1536w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/5-18x8.png 18w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/5-1140x508.png 1140w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/5-600x267.png 600w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/5.png 1879w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">What does this mean for LEDs, luminaires, systems, and designers?<\/h4>\n\n\n\n<p style=\"font-size:15px\"><strong>For LED and module manufacturers<\/strong><\/p>\n\n\n\n<p style=\"font-size:15px\">Future competitive data cannot be limited to lm\/W, CCT, and CRI.<\/p>\n\n\n\n<p style=\"font-size:15px\"><strong>SPD and \u03b1-opic \/ EDI \/ DER information will become increasingly critical.<\/strong><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p style=\"font-size:15px\"><strong>For luminaire manufacturers<\/strong><\/p>\n\n\n\n<p style=\"font-size:15px\">In the future, luminaires won\u2019t just deliver lumens into space.<\/p>\n\n\n\n<p style=\"font-size:15px\">They will deliver <strong>specific receptor-stimulation structures<\/strong> to the human eye.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p style=\"font-size:15px\"><strong>For control system manufacturers<\/strong><\/p>\n\n\n\n<p style=\"font-size:15px\">Control strategies should no longer stop at \u201cwhat time to switch to what CCT and what dimming level.\u201d<\/p>\n\n\n\n<p style=\"font-size:15px\">A more advanced control objective should be: <strong>To achieve a target balance of stimulus dose and experience<\/strong><br>for a given time, space, task, and user group.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p style=\"font-size:15px\"><strong>For designers<\/strong><\/p>\n\n\n\n<p style=\"font-size:15px\">Human-centric lighting design will go beyond \u201ccooler in the morning, warmer in the evening.\u201d<\/p>\n\n\n\n<p style=\"font-size:15px\">It will require thinking in terms of:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">Which photoreceptors this light primarily stimulates<\/li>\n\n\n\n<li style=\"font-size:15px\">What the actual dose at the eye level is<\/li>\n\n\n\n<li style=\"font-size:15px\">How to balance visual performance, circadian support, and emotional experience<\/li>\n\n\n\n<li style=\"font-size:15px\">How daylight, electric light, reflections, and viewing direction interact<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">Once designers start thinking this way, lighting design evolves from <strong>\u201cplacing fixtures\u201d to \u201cmodulating human response.\u201d<\/strong><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">Final point: the industry doesn\u2019t lack terms\u2014it lacks the ability to read the \u201cscore\u201d<\/h4>\n\n\n\n<p style=\"font-size:15px\">CAF, CS, EML, EDI \/ DER\u2026<br>These terms often feel confusing not because they lack importance, but because they are frequently discussed at the same level.<\/p>\n\n\n\n<p style=\"font-size:15px\">In reality, they answer <strong>different questions<\/strong>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">CAF \u2192 more like a <strong>spectral efficiency ratio<\/strong><\/li>\n\n\n\n<li style=\"font-size:15px\">CS \u2192 more like a <strong>specific physiological response model<\/strong><\/li>\n\n\n\n<li style=\"font-size:15px\">EML \u2192 more like an <strong>application-layer transitional language<\/strong><\/li>\n\n\n\n<li style=\"font-size:15px\">EDI \/ DER \u2192 closer to a <strong>standardized, computable, and transferable coordinate system<\/strong><\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">If the industry truly wants to move from \u201cilluminating spaces\u201d to \u201ceffectively influencing people,\u201d the next step is not to invent yet another concept\u2014 but to <strong>learn how to read this system.<\/strong><\/p>\n\n\n\n<p style=\"font-size:15px\">Illuminance tells us how bright it is. <strong>EDI \/ DER begins to tell us how light acts on humans.<\/strong> And that may well be the real starting point of the human-centric lighting era.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"577\" src=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/3-3-1024x577.jpg\" alt=\"\" class=\"wp-image-3124\" srcset=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/3-3-1024x577.jpg 1024w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/3-3-300x169.jpg 300w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/3-3-768x432.jpg 768w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/3-3-18x10.jpg 18w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/3-3-1140x642.jpg 1140w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/3-3-600x338.jpg 600w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/3-3.jpg 1364w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">CTA<\/h4>\n\n\n\n<p style=\"font-size:15px\">If your organization is exploring:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li style=\"font-size:15px\">How to upgrade LED or luminaire data from traditional photometric parameters to a language closer to human-centric lighting<\/li>\n\n\n\n<li style=\"font-size:15px\">How to integrate EDI \/ DER into product definitions, control systems, or design simulations<\/li>\n\n\n\n<li style=\"font-size:15px\">How to establish lighting evaluation methods that address circadian rhythms, visual performance, and emotional experience<\/li>\n<\/ul>\n\n\n\n<p style=\"font-size:15px\">You\u2019re welcome to get in touch.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"256\" src=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2025\/11\/1760450781036-1024x256.jpg\" alt=\"\" class=\"wp-image-2283\" srcset=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2025\/11\/1760450781036-1024x256.jpg 1024w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2025\/11\/1760450781036-300x75.jpg 300w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2025\/11\/1760450781036-768x192.jpg 768w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2025\/11\/1760450781036-1140x285.jpg 1140w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2025\/11\/1760450781036-600x150.jpg 600w, https:\/\/lightingrecipe.com\/wp-content\/uploads\/2025\/11\/1760450781036.jpg 1400w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>","protected":false},"excerpt":{"rendered":"<p>In recent years, more and more terms that sound highly technical have emerged in the lighting industry: CAF, CS, EML, m-EDI, EDI, DER\u2026 Many manufacturers, designers, consultants, and system providers have heard of them\u2014and to some extent, used them. But if we push one step further and ask: The answers are often far less clear than people assume. This reflects a very typical situation in today\u2019s lighting industry: There are more and more terms, but a true common language has not yet been established. If the industry genuinely wants to move from simply \u201clighting up spaces\u201d to accurately understanding how light affects people, then the first step is not to invent yet another new term. It is to put these commonly used metrics back into their proper context. Are these metrics really describing the same thing? Let\u2019s start with the conclusion: CAF, CS, EML, and EDI\/DER are not different names within the same framework. They originate from: Some function more like spectral efficacy ratios.Some behave more like physiological response models.Some are closer to application-level compromise metrics.And others are more like standardized, computable, and transferable baseline coordinates. So the issue is not whether these terms should exist The real issue is this: If the industry treats all of them as interchangeable \u201chealthy lighting metrics,\u201d confusion becomes inevitable. But if each metric is placed back into its proper role, many of the current ambiguities start to resolve themselves. Why is traditional lighting language no longer sufficient? In the past, the most familiar language of lighting was built around: These metrics are still essential. They primarily serve visual tasks and spatial quality: But the scope of lighting has expanded A growing body of research now shows that light also affects: Standards and position statements from the International Commission on Illumination have clearly indicated that: the traditional photopic system is not sufficient to fully describe human responses related to ipRGCs (intrinsically photosensitive retinal ganglion cells). This changes the fundamental questions The industry can no longer stop at asking: Instead, it needs to ask: This is the real context behind new metrics This shift is precisely why metrics like: have emerged. They are not just \u201cnew terminology,\u201d but attempts to extend lighting language from: visual description \u2192 human biological interaction In other words: from \u201chow the space looks\u201d to \u201chow light actually affects people.\u201d The human eye doesn\u2019t just \u201csee\u201d \u2014 it also \u201cfeels\u201d light. In the lighting industry, the most commonly discussed elements are rods and cones. That\u2019s not wrong. Rods are mainly associated with low-light (scotopic) vision. Cones are responsible for color, detail, central vision, and typical daytime visual functions. But today we know that, beyond rods and cones, there is another critically important photoreceptive pathway in the human eye: ipRGCs (intrinsically photosensitive retinal ganglion cells). These are associated with melanopsin, are more sensitive to short wavelengths, and are closely related to non-visual responses such as circadian rhythms, pupil response, and alertness. However, to be more precise, what truly needs to be considered is not three systems, but five classes of photoreceptor channels: S-cone, M-cone, L-cone, Rod, and Melanopsin \/ ipRGC. What CIE S 026:2018 establishes is a standardized metrology framework based exactly on these five photoreceptors. In other words, for the first time, the industry has a shared language that is not only about \u201cwhat can be seen,\u201d but about \u201chow light stimulates the five types of receptors.\u201d This is a critical shift. Because it means the lighting industry is moving from \u201cspatial output\u201d to \u201chuman input.\u201d What do CAF, CS, and EML actually represent? 1. CAF: closer to a \u201cspectral efficiency ratio\u201d mindset CAF (Circadian Action Factor) has long been used to compare the potential of different spectra to stimulate circadian-related responses. Its core logic is straightforward: under the same visual lighting conditions, is this spectrum more biased toward \u201ccircadian effect\u201d or \u201cvisual effect\u201d? So CAF is essentially a weighted efficiency ratio. It helps compare different SPDs under the same photopic lux to determine which produces stronger circadian-related stimulation. This approach is not without value. Its advantages are simplicity, intuitiveness, and suitability for early-stage comparisons. But it also has clear limitations: So CAF helps you understand \u201chow biased a spectrum is,\u201d but it is not suitable as a complete coordinate for human response. CAF is more like a spectral screening tool, not a full human-centric lighting language. 2. CS: closer to a \u201cspecific physiological response model\u201d CS (Circadian Stimulus) has also had significant influence in recent years, especially in North America. Its logic differs fundamentally from CAF. Rather than being a simple ratio, CS attempts\u2014through a circadian phototransduction model\u2014to map spectral stimuli onto a response scale related to melatonin suppression. UL\u2019s DG 24480 also proposes design targets based on this type of framework. The strength of CS is that: It goes beyond saying \u201cmore or less biased,\u201d and tries to quantify \u201chow strong the circadian system stimulation is.\u201d But this is also where the challenge lies. Once a metric moves from \u201cdescribing input\u201d to \u201cpredicting response,\u201d it inevitably introduces modeling assumptions: As a result, CS has been accompanied by considerable methodological debate. So a fair summary would be: CS is important, but it is better suited as an application-layer or response-layer model, rather than a foundational common coordinate system for the entire industry. 3. EML: closer to a \u201ctransitional language for application\u201d EML (Equivalent Melanopic Lux) has been widely promoted in application contexts such as WELL. Its key contribution is that it helped many people realize, for the first time: Not all lux are the same. From a communication and adoption standpoint, EML has played a significant role. It translates complex spectral\u2013receptor relationships into a format that is easier to understand and specify in project requirements. However, from a stricter standardization perspective, EML is not the ideal end state. The industry has increasingly shifted toward melanopic EDI, and further toward the more comprehensive \u03b1-opic EDI \/ DER framework, because these align better with the standardized structure defined in CIE S 026 and enable consistent use across organizations and systems. So in one sentence: EML is a bridge toward human-centric lighting\u2014but not the most suitable final coordinate system. Why are EDI \/ DER closer to a true coordinate system? Because they resemble a system that can be recorded, compared, and transmitted\u2014like a \u201cspectrum.\u201d 1. EDI: describing \u201cequivalent stimulus dose\u201d EDI (Equivalent Daylight Illuminance) can be understood as: How much illuminance from standard daylight (D65) would be required to produce the same level of stimulation for a given photoreceptor? This allows results from different spectra to be compared within a unified framework. 2. DER: describing \u201cstimulation efficiency\u201d DER (Daylight Efficacy Ratio) can be understood as: How efficient a given light is, per unit of photopic illuminance, at stimulating a specific photoreceptor. CIE TN 015:2023 clearly defines the relationship: melanopic EDI = illuminance \u00d7 melanopic DER Together, these two quantities are powerful: One is exposure-focused, the other is source-focused. This combination is exactly what manufacturers, designers, control systems, and simulation tools need. Why move from single m-EDI toward a full EDI \/ DER framework? This is not a rejection of melanopic metrics. In fact, many recent consensus recommendations are indeed centered on melanopic EDI. For example, Brown et al. (2022) suggest indoor light exposure guidelines such as: These are important. But looking further ahead: Humans do not respond to light through melanopsin alone. Visual performance, color discrimination, adaptation, spatial perception, aspects of emotional experience, and more complex neural responses all involve the combined action of rods, S\/M\/L cones, and ipRGC pathways. So if the industry aims to build a future-oriented human-centric lighting coordinate system, focusing only on m-EDI is not enough. What we need is a more complete EDI \/ DER framework: Not just melanopic\u2014but incorporating stimulation across all five photoreceptor classes into a unified language. This does not mean every project must present all five values. It means: The foundational language of the industry should leave room for a complete human model. From \u201cselling light\u201d to \u201cdescribing humans\u201d: the industry needs a new staff notation I like to use an analogy: EDI \/ DER in human-centric lighting is like musical notation in music. Musical notation is not the music itself, but it is the foundational language that allows music to be recorded, transmitted, reproduced, and collaboratively created. EDI \/ DER is similar. It is not sleep itself.Not emotion.Not comfort.Not spatial aesthetics. But it provides a way to more precisely describe: What this light is doing to the five photoreceptive channels of the human body. With such a coordinate system, many long-standing ambiguities in the industry can finally be addressed collaboratively: Without such a system, the industry easily remains stuck in vague language: More naturalCloser to daylightMore circadian-friendlyMore comfortableHealthier These terms are not useless\u2014but without an underlying framework, they struggle to become a shared language across organizations and product chains. The real value of EDI \/ DER lies in this: For the first time, \u201chow light affects humans\u201d can be written down\u2014like a score. What does this mean for LEDs, luminaires, systems, and designers? For LED and module manufacturers Future competitive data cannot be limited to lm\/W, CCT, and CRI. SPD and \u03b1-opic \/ EDI \/ DER information will become increasingly critical. For luminaire manufacturers In the future, luminaires won\u2019t just deliver lumens into space. They will deliver specific receptor-stimulation structures to the human eye. For control system manufacturers Control strategies should no longer stop at \u201cwhat time to switch to what CCT and what dimming level.\u201d A more advanced control objective should be: To achieve a target balance of stimulus dose and experiencefor a given time, space, task, and user group. For designers Human-centric lighting design will go beyond \u201ccooler in the morning, warmer in the evening.\u201d It will require thinking in terms of: Once designers start thinking this way, lighting design evolves from \u201cplacing fixtures\u201d to \u201cmodulating human response.\u201d Final point: the industry doesn\u2019t lack terms\u2014it lacks the ability to read the \u201cscore\u201d CAF, CS, EML, EDI \/ DER\u2026These terms often feel confusing not because they lack importance, but because they are frequently discussed at the same level. In reality, they answer different questions: If the industry truly wants to move from \u201cilluminating spaces\u201d to \u201ceffectively influencing people,\u201d the next step is not to invent yet another concept\u2014 but to learn how to read this system. Illuminance tells us how bright it is. EDI \/ DER begins to tell us how light acts on humans. And that may well be the real starting point of the human-centric lighting era. CTA If your organization is exploring: You\u2019re welcome to get in touch.<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_glsr_average":0,"_glsr_ranking":0,"_glsr_reviews":0,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[],"tags":[],"class_list":["post-3117","post","type-post","status-publish","format-standard","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.0 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>CAF, CS, EML, EDI\/DER\u2026 are these commonly referenced metrics actually talking about the same thing? -<\/title>\n<meta name=\"robots\" content=\"noindex, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<meta property=\"og:locale\" content=\"zh_TW\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"CAF, CS, EML, EDI\/DER\u2026 are these commonly referenced metrics actually talking about the same thing? -\" \/>\n<meta property=\"og:description\" content=\"In recent years, more and more terms that sound highly technical have emerged in the lighting industry: CAF, CS, EML, m-EDI, EDI, DER\u2026 Many manufacturers, designers, consultants, and system providers have heard of them\u2014and to some extent, used them. But if we push one step further and ask: The answers are often far less clear than people assume. This reflects a very typical situation in today\u2019s lighting industry: There are more and more terms, but a true common language has not yet been established. If the industry genuinely wants to move from simply \u201clighting up spaces\u201d to accurately understanding how light affects people, then the first step is not to invent yet another new term. It is to put these commonly used metrics back into their proper context. Are these metrics really describing the same thing? Let\u2019s start with the conclusion: CAF, CS, EML, and EDI\/DER are not different names within the same framework. They originate from: Some function more like spectral efficacy ratios.Some behave more like physiological response models.Some are closer to application-level compromise metrics.And others are more like standardized, computable, and transferable baseline coordinates. So the issue is not whether these terms should exist The real issue is this: If the industry treats all of them as interchangeable \u201chealthy lighting metrics,\u201d confusion becomes inevitable. But if each metric is placed back into its proper role, many of the current ambiguities start to resolve themselves. Why is traditional lighting language no longer sufficient? In the past, the most familiar language of lighting was built around: These metrics are still essential. They primarily serve visual tasks and spatial quality: But the scope of lighting has expanded A growing body of research now shows that light also affects: Standards and position statements from the International Commission on Illumination have clearly indicated that: the traditional photopic system is not sufficient to fully describe human responses related to ipRGCs (intrinsically photosensitive retinal ganglion cells). This changes the fundamental questions The industry can no longer stop at asking: Instead, it needs to ask: This is the real context behind new metrics This shift is precisely why metrics like: have emerged. They are not just \u201cnew terminology,\u201d but attempts to extend lighting language from: visual description \u2192 human biological interaction In other words: from \u201chow the space looks\u201d to \u201chow light actually affects people.\u201d The human eye doesn\u2019t just \u201csee\u201d \u2014 it also \u201cfeels\u201d light. In the lighting industry, the most commonly discussed elements are rods and cones. That\u2019s not wrong. Rods are mainly associated with low-light (scotopic) vision. Cones are responsible for color, detail, central vision, and typical daytime visual functions. But today we know that, beyond rods and cones, there is another critically important photoreceptive pathway in the human eye: ipRGCs (intrinsically photosensitive retinal ganglion cells). These are associated with melanopsin, are more sensitive to short wavelengths, and are closely related to non-visual responses such as circadian rhythms, pupil response, and alertness. However, to be more precise, what truly needs to be considered is not three systems, but five classes of photoreceptor channels: S-cone, M-cone, L-cone, Rod, and Melanopsin \/ ipRGC. What CIE S 026:2018 establishes is a standardized metrology framework based exactly on these five photoreceptors. In other words, for the first time, the industry has a shared language that is not only about \u201cwhat can be seen,\u201d but about \u201chow light stimulates the five types of receptors.\u201d This is a critical shift. Because it means the lighting industry is moving from \u201cspatial output\u201d to \u201chuman input.\u201d What do CAF, CS, and EML actually represent? 1. CAF: closer to a \u201cspectral efficiency ratio\u201d mindset CAF (Circadian Action Factor) has long been used to compare the potential of different spectra to stimulate circadian-related responses. Its core logic is straightforward: under the same visual lighting conditions, is this spectrum more biased toward \u201ccircadian effect\u201d or \u201cvisual effect\u201d? So CAF is essentially a weighted efficiency ratio. It helps compare different SPDs under the same photopic lux to determine which produces stronger circadian-related stimulation. This approach is not without value. Its advantages are simplicity, intuitiveness, and suitability for early-stage comparisons. But it also has clear limitations: So CAF helps you understand \u201chow biased a spectrum is,\u201d but it is not suitable as a complete coordinate for human response. CAF is more like a spectral screening tool, not a full human-centric lighting language. 2. CS: closer to a \u201cspecific physiological response model\u201d CS (Circadian Stimulus) has also had significant influence in recent years, especially in North America. Its logic differs fundamentally from CAF. Rather than being a simple ratio, CS attempts\u2014through a circadian phototransduction model\u2014to map spectral stimuli onto a response scale related to melatonin suppression. UL\u2019s DG 24480 also proposes design targets based on this type of framework. The strength of CS is that: It goes beyond saying \u201cmore or less biased,\u201d and tries to quantify \u201chow strong the circadian system stimulation is.\u201d But this is also where the challenge lies. Once a metric moves from \u201cdescribing input\u201d to \u201cpredicting response,\u201d it inevitably introduces modeling assumptions: As a result, CS has been accompanied by considerable methodological debate. So a fair summary would be: CS is important, but it is better suited as an application-layer or response-layer model, rather than a foundational common coordinate system for the entire industry. 3. EML: closer to a \u201ctransitional language for application\u201d EML (Equivalent Melanopic Lux) has been widely promoted in application contexts such as WELL. Its key contribution is that it helped many people realize, for the first time: Not all lux are the same. From a communication and adoption standpoint, EML has played a significant role. It translates complex spectral\u2013receptor relationships into a format that is easier to understand and specify in project requirements. However, from a stricter standardization perspective, EML is not the ideal end state. The industry has increasingly shifted toward melanopic EDI, and further toward the more comprehensive \u03b1-opic EDI \/ DER framework, because these align better with the standardized structure defined in CIE S 026 and enable consistent use across organizations and systems. So in one sentence: EML is a bridge toward human-centric lighting\u2014but not the most suitable final coordinate system. Why are EDI \/ DER closer to a true coordinate system? Because they resemble a system that can be recorded, compared, and transmitted\u2014like a \u201cspectrum.\u201d 1. EDI: describing \u201cequivalent stimulus dose\u201d EDI (Equivalent Daylight Illuminance) can be understood as: How much illuminance from standard daylight (D65) would be required to produce the same level of stimulation for a given photoreceptor? This allows results from different spectra to be compared within a unified framework. 2. DER: describing \u201cstimulation efficiency\u201d DER (Daylight Efficacy Ratio) can be understood as: How efficient a given light is, per unit of photopic illuminance, at stimulating a specific photoreceptor. CIE TN 015:2023 clearly defines the relationship: melanopic EDI = illuminance \u00d7 melanopic DER Together, these two quantities are powerful: One is exposure-focused, the other is source-focused. This combination is exactly what manufacturers, designers, control systems, and simulation tools need. Why move from single m-EDI toward a full EDI \/ DER framework? This is not a rejection of melanopic metrics. In fact, many recent consensus recommendations are indeed centered on melanopic EDI. For example, Brown et al. (2022) suggest indoor light exposure guidelines such as: These are important. But looking further ahead: Humans do not respond to light through melanopsin alone. Visual performance, color discrimination, adaptation, spatial perception, aspects of emotional experience, and more complex neural responses all involve the combined action of rods, S\/M\/L cones, and ipRGC pathways. So if the industry aims to build a future-oriented human-centric lighting coordinate system, focusing only on m-EDI is not enough. What we need is a more complete EDI \/ DER framework: Not just melanopic\u2014but incorporating stimulation across all five photoreceptor classes into a unified language. This does not mean every project must present all five values. It means: The foundational language of the industry should leave room for a complete human model. From \u201cselling light\u201d to \u201cdescribing humans\u201d: the industry needs a new staff notation I like to use an analogy: EDI \/ DER in human-centric lighting is like musical notation in music. Musical notation is not the music itself, but it is the foundational language that allows music to be recorded, transmitted, reproduced, and collaboratively created. EDI \/ DER is similar. It is not sleep itself.Not emotion.Not comfort.Not spatial aesthetics. But it provides a way to more precisely describe: What this light is doing to the five photoreceptive channels of the human body. With such a coordinate system, many long-standing ambiguities in the industry can finally be addressed collaboratively: Without such a system, the industry easily remains stuck in vague language: More naturalCloser to daylightMore circadian-friendlyMore comfortableHealthier These terms are not useless\u2014but without an underlying framework, they struggle to become a shared language across organizations and product chains. The real value of EDI \/ DER lies in this: For the first time, \u201chow light affects humans\u201d can be written down\u2014like a score. What does this mean for LEDs, luminaires, systems, and designers? For LED and module manufacturers Future competitive data cannot be limited to lm\/W, CCT, and CRI. SPD and \u03b1-opic \/ EDI \/ DER information will become increasingly critical. For luminaire manufacturers In the future, luminaires won\u2019t just deliver lumens into space. They will deliver specific receptor-stimulation structures to the human eye. For control system manufacturers Control strategies should no longer stop at \u201cwhat time to switch to what CCT and what dimming level.\u201d A more advanced control objective should be: To achieve a target balance of stimulus dose and experiencefor a given time, space, task, and user group. For designers Human-centric lighting design will go beyond \u201ccooler in the morning, warmer in the evening.\u201d It will require thinking in terms of: Once designers start thinking this way, lighting design evolves from \u201cplacing fixtures\u201d to \u201cmodulating human response.\u201d Final point: the industry doesn\u2019t lack terms\u2014it lacks the ability to read the \u201cscore\u201d CAF, CS, EML, EDI \/ DER\u2026These terms often feel confusing not because they lack importance, but because they are frequently discussed at the same level. In reality, they answer different questions: If the industry truly wants to move from \u201cilluminating spaces\u201d to \u201ceffectively influencing people,\u201d the next step is not to invent yet another concept\u2014 but to learn how to read this system. Illuminance tells us how bright it is. EDI \/ DER begins to tell us how light acts on humans. And that may well be the real starting point of the human-centric lighting era. CTA If your organization is exploring: You\u2019re welcome to get in touch.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/lightingrecipe.com\/zh\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/\" \/>\n<meta property=\"article:published_time\" content=\"2026-04-30T07:41:41+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-04-30T07:42:28+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1858\" \/>\n\t<meta property=\"og:image:height\" content=\"576\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"LRS Admin\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"\u4f5c\u8005:\" \/>\n\t<meta name=\"twitter:data1\" content=\"LRS Admin\" \/>\n\t<meta name=\"twitter:label2\" content=\"\u9810\u4f30\u95b1\u8b80\u6642\u9593\" \/>\n\t<meta name=\"twitter:data2\" content=\"11 \u5206\u9418\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/lightingrecipe.com\\\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/lightingrecipe.com\\\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\\\/\"},\"author\":{\"name\":\"LRS Admin\",\"@id\":\"https:\\\/\\\/lightingrecipe.com\\\/#\\\/schema\\\/person\\\/d8fc98bd754facede814f69c45e6ab7a\"},\"headline\":\"CAF, CS, EML, EDI\\\/DER\u2026 are these commonly referenced metrics actually talking about the same thing?\",\"datePublished\":\"2026-04-30T07:41:41+00:00\",\"dateModified\":\"2026-04-30T07:42:28+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/lightingrecipe.com\\\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\\\/\"},\"wordCount\":2159,\"commentCount\":0,\"image\":{\"@id\":\"https:\\\/\\\/lightingrecipe.com\\\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/lightingrecipe.com\\\/wp-content\\\/uploads\\\/2026\\\/04\\\/1-3-1024x317.jpg\",\"inLanguage\":\"zh-TW\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\\\/\\\/lightingrecipe.com\\\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\\\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/lightingrecipe.com\\\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\\\/\",\"url\":\"https:\\\/\\\/lightingrecipe.com\\\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\\\/\",\"name\":\"CAF, CS, EML, EDI\\\/DER\u2026 are these commonly referenced metrics actually talking about the same thing? 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-","robots":{"index":"noindex","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"og_locale":"zh_TW","og_type":"article","og_title":"CAF, CS, EML, EDI\/DER\u2026 are these commonly referenced metrics actually talking about the same thing? -","og_description":"In recent years, more and more terms that sound highly technical have emerged in the lighting industry: CAF, CS, EML, m-EDI, EDI, DER\u2026 Many manufacturers, designers, consultants, and system providers have heard of them\u2014and to some extent, used them. But if we push one step further and ask: The answers are often far less clear than people assume. This reflects a very typical situation in today\u2019s lighting industry: There are more and more terms, but a true common language has not yet been established. If the industry genuinely wants to move from simply \u201clighting up spaces\u201d to accurately understanding how light affects people, then the first step is not to invent yet another new term. It is to put these commonly used metrics back into their proper context. Are these metrics really describing the same thing? Let\u2019s start with the conclusion: CAF, CS, EML, and EDI\/DER are not different names within the same framework. They originate from: Some function more like spectral efficacy ratios.Some behave more like physiological response models.Some are closer to application-level compromise metrics.And others are more like standardized, computable, and transferable baseline coordinates. So the issue is not whether these terms should exist The real issue is this: If the industry treats all of them as interchangeable \u201chealthy lighting metrics,\u201d confusion becomes inevitable. But if each metric is placed back into its proper role, many of the current ambiguities start to resolve themselves. Why is traditional lighting language no longer sufficient? In the past, the most familiar language of lighting was built around: These metrics are still essential. They primarily serve visual tasks and spatial quality: But the scope of lighting has expanded A growing body of research now shows that light also affects: Standards and position statements from the International Commission on Illumination have clearly indicated that: the traditional photopic system is not sufficient to fully describe human responses related to ipRGCs (intrinsically photosensitive retinal ganglion cells). This changes the fundamental questions The industry can no longer stop at asking: Instead, it needs to ask: This is the real context behind new metrics This shift is precisely why metrics like: have emerged. They are not just \u201cnew terminology,\u201d but attempts to extend lighting language from: visual description \u2192 human biological interaction In other words: from \u201chow the space looks\u201d to \u201chow light actually affects people.\u201d The human eye doesn\u2019t just \u201csee\u201d \u2014 it also \u201cfeels\u201d light. In the lighting industry, the most commonly discussed elements are rods and cones. That\u2019s not wrong. Rods are mainly associated with low-light (scotopic) vision. Cones are responsible for color, detail, central vision, and typical daytime visual functions. But today we know that, beyond rods and cones, there is another critically important photoreceptive pathway in the human eye: ipRGCs (intrinsically photosensitive retinal ganglion cells). These are associated with melanopsin, are more sensitive to short wavelengths, and are closely related to non-visual responses such as circadian rhythms, pupil response, and alertness. However, to be more precise, what truly needs to be considered is not three systems, but five classes of photoreceptor channels: S-cone, M-cone, L-cone, Rod, and Melanopsin \/ ipRGC. What CIE S 026:2018 establishes is a standardized metrology framework based exactly on these five photoreceptors. In other words, for the first time, the industry has a shared language that is not only about \u201cwhat can be seen,\u201d but about \u201chow light stimulates the five types of receptors.\u201d This is a critical shift. Because it means the lighting industry is moving from \u201cspatial output\u201d to \u201chuman input.\u201d What do CAF, CS, and EML actually represent? 1. CAF: closer to a \u201cspectral efficiency ratio\u201d mindset CAF (Circadian Action Factor) has long been used to compare the potential of different spectra to stimulate circadian-related responses. Its core logic is straightforward: under the same visual lighting conditions, is this spectrum more biased toward \u201ccircadian effect\u201d or \u201cvisual effect\u201d? So CAF is essentially a weighted efficiency ratio. It helps compare different SPDs under the same photopic lux to determine which produces stronger circadian-related stimulation. This approach is not without value. Its advantages are simplicity, intuitiveness, and suitability for early-stage comparisons. But it also has clear limitations: So CAF helps you understand \u201chow biased a spectrum is,\u201d but it is not suitable as a complete coordinate for human response. CAF is more like a spectral screening tool, not a full human-centric lighting language. 2. CS: closer to a \u201cspecific physiological response model\u201d CS (Circadian Stimulus) has also had significant influence in recent years, especially in North America. Its logic differs fundamentally from CAF. Rather than being a simple ratio, CS attempts\u2014through a circadian phototransduction model\u2014to map spectral stimuli onto a response scale related to melatonin suppression. UL\u2019s DG 24480 also proposes design targets based on this type of framework. The strength of CS is that: It goes beyond saying \u201cmore or less biased,\u201d and tries to quantify \u201chow strong the circadian system stimulation is.\u201d But this is also where the challenge lies. Once a metric moves from \u201cdescribing input\u201d to \u201cpredicting response,\u201d it inevitably introduces modeling assumptions: As a result, CS has been accompanied by considerable methodological debate. So a fair summary would be: CS is important, but it is better suited as an application-layer or response-layer model, rather than a foundational common coordinate system for the entire industry. 3. EML: closer to a \u201ctransitional language for application\u201d EML (Equivalent Melanopic Lux) has been widely promoted in application contexts such as WELL. Its key contribution is that it helped many people realize, for the first time: Not all lux are the same. From a communication and adoption standpoint, EML has played a significant role. It translates complex spectral\u2013receptor relationships into a format that is easier to understand and specify in project requirements. However, from a stricter standardization perspective, EML is not the ideal end state. The industry has increasingly shifted toward melanopic EDI, and further toward the more comprehensive \u03b1-opic EDI \/ DER framework, because these align better with the standardized structure defined in CIE S 026 and enable consistent use across organizations and systems. So in one sentence: EML is a bridge toward human-centric lighting\u2014but not the most suitable final coordinate system. Why are EDI \/ DER closer to a true coordinate system? Because they resemble a system that can be recorded, compared, and transmitted\u2014like a \u201cspectrum.\u201d 1. EDI: describing \u201cequivalent stimulus dose\u201d EDI (Equivalent Daylight Illuminance) can be understood as: How much illuminance from standard daylight (D65) would be required to produce the same level of stimulation for a given photoreceptor? This allows results from different spectra to be compared within a unified framework. 2. DER: describing \u201cstimulation efficiency\u201d DER (Daylight Efficacy Ratio) can be understood as: How efficient a given light is, per unit of photopic illuminance, at stimulating a specific photoreceptor. CIE TN 015:2023 clearly defines the relationship: melanopic EDI = illuminance \u00d7 melanopic DER Together, these two quantities are powerful: One is exposure-focused, the other is source-focused. This combination is exactly what manufacturers, designers, control systems, and simulation tools need. Why move from single m-EDI toward a full EDI \/ DER framework? This is not a rejection of melanopic metrics. In fact, many recent consensus recommendations are indeed centered on melanopic EDI. For example, Brown et al. (2022) suggest indoor light exposure guidelines such as: These are important. But looking further ahead: Humans do not respond to light through melanopsin alone. Visual performance, color discrimination, adaptation, spatial perception, aspects of emotional experience, and more complex neural responses all involve the combined action of rods, S\/M\/L cones, and ipRGC pathways. So if the industry aims to build a future-oriented human-centric lighting coordinate system, focusing only on m-EDI is not enough. What we need is a more complete EDI \/ DER framework: Not just melanopic\u2014but incorporating stimulation across all five photoreceptor classes into a unified language. This does not mean every project must present all five values. It means: The foundational language of the industry should leave room for a complete human model. From \u201cselling light\u201d to \u201cdescribing humans\u201d: the industry needs a new staff notation I like to use an analogy: EDI \/ DER in human-centric lighting is like musical notation in music. Musical notation is not the music itself, but it is the foundational language that allows music to be recorded, transmitted, reproduced, and collaboratively created. EDI \/ DER is similar. It is not sleep itself.Not emotion.Not comfort.Not spatial aesthetics. But it provides a way to more precisely describe: What this light is doing to the five photoreceptive channels of the human body. With such a coordinate system, many long-standing ambiguities in the industry can finally be addressed collaboratively: Without such a system, the industry easily remains stuck in vague language: More naturalCloser to daylightMore circadian-friendlyMore comfortableHealthier These terms are not useless\u2014but without an underlying framework, they struggle to become a shared language across organizations and product chains. The real value of EDI \/ DER lies in this: For the first time, \u201chow light affects humans\u201d can be written down\u2014like a score. What does this mean for LEDs, luminaires, systems, and designers? For LED and module manufacturers Future competitive data cannot be limited to lm\/W, CCT, and CRI. SPD and \u03b1-opic \/ EDI \/ DER information will become increasingly critical. For luminaire manufacturers In the future, luminaires won\u2019t just deliver lumens into space. They will deliver specific receptor-stimulation structures to the human eye. For control system manufacturers Control strategies should no longer stop at \u201cwhat time to switch to what CCT and what dimming level.\u201d A more advanced control objective should be: To achieve a target balance of stimulus dose and experiencefor a given time, space, task, and user group. For designers Human-centric lighting design will go beyond \u201ccooler in the morning, warmer in the evening.\u201d It will require thinking in terms of: Once designers start thinking this way, lighting design evolves from \u201cplacing fixtures\u201d to \u201cmodulating human response.\u201d Final point: the industry doesn\u2019t lack terms\u2014it lacks the ability to read the \u201cscore\u201d CAF, CS, EML, EDI \/ DER\u2026These terms often feel confusing not because they lack importance, but because they are frequently discussed at the same level. In reality, they answer different questions: If the industry truly wants to move from \u201cilluminating spaces\u201d to \u201ceffectively influencing people,\u201d the next step is not to invent yet another concept\u2014 but to learn how to read this system. Illuminance tells us how bright it is. EDI \/ DER begins to tell us how light acts on humans. And that may well be the real starting point of the human-centric lighting era. CTA If your organization is exploring: You\u2019re welcome to get in touch.","og_url":"https:\/\/lightingrecipe.com\/zh\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/","article_published_time":"2026-04-30T07:41:41+00:00","article_modified_time":"2026-04-30T07:42:28+00:00","og_image":[{"width":1858,"height":576,"url":"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3.jpg","type":"image\/jpeg"}],"author":"LRS Admin","twitter_card":"summary_large_image","twitter_misc":{"\u4f5c\u8005:":"LRS Admin","\u9810\u4f30\u95b1\u8b80\u6642\u9593":"11 \u5206\u9418"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/lightingrecipe.com\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/#article","isPartOf":{"@id":"https:\/\/lightingrecipe.com\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/"},"author":{"name":"LRS Admin","@id":"https:\/\/lightingrecipe.com\/#\/schema\/person\/d8fc98bd754facede814f69c45e6ab7a"},"headline":"CAF, CS, EML, EDI\/DER\u2026 are these commonly referenced metrics actually talking about the same thing?","datePublished":"2026-04-30T07:41:41+00:00","dateModified":"2026-04-30T07:42:28+00:00","mainEntityOfPage":{"@id":"https:\/\/lightingrecipe.com\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/"},"wordCount":2159,"commentCount":0,"image":{"@id":"https:\/\/lightingrecipe.com\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/#primaryimage"},"thumbnailUrl":"https:\/\/lightingrecipe.com\/wp-content\/uploads\/2026\/04\/1-3-1024x317.jpg","inLanguage":"zh-TW","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/lightingrecipe.com\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/#respond"]}]},{"@type":"WebPage","@id":"https:\/\/lightingrecipe.com\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/","url":"https:\/\/lightingrecipe.com\/caf-cs-eml-edi-der-are-these-commonly-referenced-metrics-actually-talking-about-the-same-thing\/","name":"CAF, CS, EML, EDI\/DER\u2026 are these commonly referenced metrics actually talking about the same thing? 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